The present invention relates to mine roof support systems and, more particularly, to bolting assemblies used in conjunction with resin anchoring systems.
Among the various types of rock reinforcing systems such as utilized, for example, in supporting mine roofs, is that wherein a plate is held against the roof surface by the head of a bolt which is securely anchored by means of a resin grout in a blind hole drilled for that purpose in the rock face. The resin is commonly provided in a rupturable package together with, but physically separated from, a catalyst, curing agent, or the like. The resin package is inserted in the hole ahead of the bolt which is forced into the package and rotated to rupture the package and mix the two components carried thereby.
In some prior art constructions, the portion of the bolt or bar which extends outside the drill hole after installation is threaded and a nut installed thereon for tightening into engagement with the support plate after the resin has hardened. The bolt anchoring systems of U.S Pat. Nos. 3,940,941 and 3,979,918, for example, are of this type. In other systems, such as those of U.S. Pat. Nos. 3,877,235 and 4,023,373, the end of the bolt which is inserted in the hole is threaded into a hollow member which is anchored in the hole by the resin grouting. In both of the aforementioned anchoring systems the end of the bar which is inserted into the hole is advanced into the resin package to rupture the compartment walls and rotated to mix the two components. Rotation of the bar and threaded member (whether the latter is outside or inside the drill hole) is effected as a single unit, i.e., there is no relative rotation of the two, as rupture of the resin package and mixing of the components is effected. Rotation is then halted as the mixed resin grout which has been described about the anchoring member for a portion of its length within the drill hole hardens. After a sufficient amount of hardening has taken place, torque is again applied, producing relative rotation between the bar or bolt and the threaded member.
In all of these aforementioned patents, means are provided for restraining relative rotational movement between the bolt or bar and the member threaded on one end or the other thereof during resin component mixing. Such means are releasable, however, to permit relative rotation upon the application of a predetermined excess torque to one member as the other is held stationary, as by the hardened resin grout. In Pat. No. 3,979,918 the releasable, relative-rotation restraining means is provided by a differential in thread pitch between the threaded end of the bar extending outside the hold and the nut threaded thereon. Alternatively, one end of the nut is deformed at several places about the periphery of the threaded opening by forming indentations in the face of the nut, which may then be threaded on the bolt until the deformed end is flush with the end of the bolt. Further relative rotation is restrained until an excess torque is applied to the nut while holding the bolt rotationally stationary.
In the anchoring systems of Pat. Nos. 3,877,235 and 4,023,373 the end of the bolt which is inserted into the drill hole is threaded into an internally threaded member which is inserted into the hole ahead of the bolt for engagement with the resin package at the inner end of the hole. In both patents means are provided to restrain rotational advancement of the bolt into the internally threaded member past a predetermined point. When this point is reached the bolt and member rotate as a single unit until the resin is mixed and hardened to anchor the internally threaded member in a fixed position. The application of excess torque to the bolt will then overcome the restraining means and permit rotation and threaded advancement of the bolt into the member, thereby bringing the support plate into engagement with the wall to be supported.
It is an object of the present invention to provide an improved bolt anchoring system of the resin grouted type utilizing a plate-supporting bolt and a resin-engaging reinforcing bar with an internally threaded collar having unique releasable relative-rotation restraining means.
Another object is to provide a resin-anchored rock bolting system wherein a collar, internally threaded at both ends, is used to join a rock bolt and reinforcing bar, and the rotational restraining means are incorporated without significantly affecting the manufacturing cost.
Still another object is to provide a rock bolting system having the aforementioned elements wherein the excess torque required to overcome the relative rotation restraining means may be easily varied and closely controlled in manufacture.
In a more general sense, the principal object is to provide a novel and improved resin grouted rock bolting system.
Other objects will in part be obvious and will in part appear hereinafter.